The present invention relates generally to the field of semiconductor processing equipment and more specifically to a method and apparatus for eliminating contaminants and residues from inside a vacuum exhaust line connected to a processing chamber and to a method and apparatus for reducing perfluorocompound (PFC) gas emissions from a processing chamber.
During chemical vapor deposition (CVD) processing, deposition gases are released inside a processing chamber to form a thin film layer on the surface of a substrate being processed. Unwanted deposition on areas such as the walls of the processing chamber also occurs during such CVD processes. Because the residence time in the chamber of individual molecules in these deposition gases is relatively short, however, only a small portion of the molecules released into the chamber are consumed in the deposition process and deposited on either the wafer or chamber walls.
The unconsumed gas molecules are pumped out of the chamber along with partially reacted compounds and reaction byproducts through a vacuum exhaust line that is commonly referred to as the xe2x80x9cforeline.xe2x80x9d Many of the compounds in this exhausted gas are still in highly reactive states and/or contain residues or particulate matter that can form unwanted deposits in the foreline. Given time, this deposition build-up of powdery residue and/or particulate matter presents a problem. First, the matter is often a pyrophoric substance that may present problems when the vacuum seal is broken and the foreline is exposed to ambient conditions during standard, periodic cleaning operations. Second, if enough of the deposition material builds-up in the foreline, the foreline and/or its associated vacuum pump may clog if it is not appropriately cleaned. Even when periodically cleaned, matter build-up interferes with normal operation of the vacuum pump and can drastically shorten the useful life of the pump. Also, the solid matter may backwash from the foreline into the processing chamber and contaminate processing steps adversely effecting wafer yield.
To avoid these problems, the inside surface of the foreline is regularly cleaned to remove the deposited material. This procedure is performed during a standard chamber clean operation that is employed to remove unwanted deposition material from the chamber walls and similar areas of the processing chamber. Common chamber cleaning techniques include the use of an etching gas, such as fluorine, to remove the deposited material from the chamber walls and other areas. The etching gas is introduced into the chamber and a plasma is formed so that the etching gas reacts with and removes the deposited material from the chamber walls. Such cleaning procedures are commonly performed between deposition steps for every wafer or every N wafers.
Removal of deposition material from chamber walls is relatively straightforward in that the plasma is created within the chamber in an area proximate to the deposited material. Removal of deposition material from the foreline is more difficult because the foreline is downstream from the processing chamber. In a fixed time period, most points within the processing chamber come in contact with more of the etchant fluorine atoms than do points within the foreline. Thus, in a fixed time period, the chamber may be adequately cleaned by the clean process while residue and similar deposits remain in the foreline.
To attempt to adequately clean the foreline, the duration of the clean operation must be increased. Increasing the length of the clean operation, however, is undesirable because it adversely effects wafer throughput. Also, such residue build-up can be cleaned only to the extent that reactants from the clean step are exhausted into the foreline in a state that they may react with the residue in the foreline. In some systems and applications, the lifetime of the exhausted reactants is not sufficient to reach the end or even middle portions of the foreline. In these systems and applications, residue build-up is even more of a concern. Accordingly, there is a need for an apparatus for efficiently and thoroughly cleaning the foreline in a semiconductor processing system and a method of doing the same.
One approach that has been employed to clean the foreline relies on a scrubbing system that uses plasma enhanced CVD techniques to extract reactive components in the exhaust gas as film deposits on electrode surfaces. The scrubbing system is designed to maximize the removal of reactants as a solid film and uses large surface area spiral electrodes. The spiral electrodes are contained within a removable canister that is positioned near the end of the foreline between the blower pump and mechanical pump. After a sufficient amount of solid waste has built up on the electrodes, the canisters may be removed for disposal and replacement.
Problems exist in this prior art method in that the system relies on the large surface area of the electrodes to provide an area for deposited solid matter to collect. To accommodate the large surface area of the electrodes, the system is necessarily large and bulky. Furthermore, extra expenses are incurred in the operation of this prior art scrubber system since the removable canister is a disposable product that must be replaced and properly disposed. Also, the scrubbing system is located downstream from a beginning portion of the vacuum foreline and thus does not ensure removal of powdery material or particulate matter that builds-up in this portion of the line.
Other approaches to remove particle build-up have relied on creation of a plasma within a particle collection chamber. Basically, these approaches use electrostatic, thermophoretic and/or gravitational forces to collect particles and other solid matter within a collection chamber. The collected particulate matter is then converted to gaseous products that may be pumped through the vacuum line when etchant gases, such as fluorine, are exhausted from the chamber through the vacuum line during a clean step. The conversion process in these devices includes the creation of a plasma by one of several different methods including the use of microwave power, capacitively-coupled electrodes or an induction field. Examples of devices using these approaches are described in Published European Patent Application Nos. 96306536.2, entitled xe2x80x9cMETHOD AND APPARATUS FOR CLEANING A VACUUM LINE IN A CVD SYSTEMxe2x80x9d; 97308660.6, entitled xe2x80x9cPARALLEL PLATE APPARATUS FOR IN-SITU VACUUM LINE CLEANING FOR SUBSTRATE PROCESSING EQUIPMENTxe2x80x9d; 96309542.7, entitled xe2x80x9cMETHOD AND APPARATUS FOR REDUCING PERFLUOROCOMPOUND GASES FROM SUBSTRATE PROCESSING EQUIPMENT EMISSIONSxe2x80x9d and 97118103.7, entitled xe2x80x9cMICROWAVE APPARATUS FOR IN-SITU VACUUM LINE CLEANING FOR SUBSTRATE PROCESSING EQUIPMENTxe2x80x9d each of which are assigned to Applied Materials, the assignee of the present invention.
Despite the development of the devices described in the three Applied Material""s patent applications described above, other improved methods and devices for cleaning substrate chamber forelines are desirable.
The present invention provides a new and improved method and device for cleaning substrate chamber forelines. The invention solves many of the problems of some prior art devices described above and provides an improved apparatus that substantially prevents particulate matter and other residual material from building up in an exhaust line. Powder residue and other particulate matter that would otherwise collect in the vacuum line during deposition steps is trapped in a collection chamber where it is held until a subsequent clean step. Fluorine, or other etchant radicals introduced into the chamber in the clean step make their way through the exhaust line into the collection chamber where they react with the trapped particles converting them into gaseous products that can be readily pumped through the vacuum line. The invention also provides a method for preventing the formation of and ensuring removal of such particulate material from within vacuum line.
The present invention provides improved particle control without the need to generate a separate plasma within the particle collector thus saving operational and construction costs as compared to devices that rely on generation of a plasma within the device. Also, the present invention achieves these results while being process transparent. That is, in preferred embodiments, operation of the present invention takes no additional processing time to either prevent particulate matter from building up within the foreline or to clean the built-up particulate matter from the collection chamber.
In one embodiment of the apparatus of the present invention, the apparatus includes a vessel chamber having an inlet, an outlet and a fluid conduit therebetween that fluidly-couples the outlet with the inlet. The fluid conduit includes first and second collection sections. The first collection section includes a first plurality of electrodes aligned parallel to a first plane and the second collection section includes a first gas passageway defining a path of flow in a first direction for gases passing through the fluid conduit and a second gas passageway defining a flow path in a second direction different than the first direction. The electrodes in the first section are connected to a voltage differential to form an electrostatic particle collector that traps electrically charged particles and particulate matter flowing through the fluid conduit.
Particles are collected within the fluid conduit during substrate processing operations such as CVD deposition steps. Then, during a chamber clean operation, unreacted etchant gases used to clean the substrate processing chamber are exhausted through the foreline and into the apparatus of the present invention where they react with the collected particles and/or powder to convert the solid material into gaseous matter. The gaseous matter can be pumped through the foreline without damaging the vacuum pump or other processing equipment.
In a preferred embodiment of the apparatus of the present invention, the second collection section includes a second plurality of electrodes, connected to the voltage differential, that define the first and second gas passages and that are aligned parallel to a second plane that intersects the first plane. In a more preferred embodiment, the second plane is substantially perpendicular to the first plane and the first direction is substantially opposite in direction to the second direction.
In another preferred embodiment, at least some of the first and/or second pluralities of electrodes are connected to a heater that heats the trapped particles and facilitates breakdown of the particles into gaseous products during subsequent clean cycles.
In still other preferred embodiments, the first plurality of electrodes includes outer and inner electrodes extending toward each other in an interdigitated manner. The outer electrodes fan out from an exterior wall of the fluid conduit and the inner electrodes fan out from an interior shaft extending through a center portion of the apparatus. In this embodiment, the second plurality of electrodes can also include outer and inner electrodes extending toward each other in an interdigitated manner with the outer electrodes fanning out from an exterior wall and the inner electrodes extending out from an interior shaft of the apparatus.
These and other embodiments of the present invention, as well as its advantages and features are described in more detail in conjunction with the text below and attached figures.